As part of the modernization of the US Air Traffic Control system known as NextGen, as well as deployments in Australia, on the Atlantic Oceanic routes, and elsewhere, Automatic Dependent Surveillance—Broadcast (ADS-B) is poised to become a key part of the surveillance infrastructure for aviation around the world. In ADS-B, each equipped vehicle transmits its position, altitude, velocity, identity and other information at regular intervals through an onboard transmitter (ADS-B Out). Nearby equipped vehicles receive these position reports through a receiver and can use them to avoid colliding with the reporting vehicle (ADS-B In). Air traffic control also may receive the position reports and use them to coordinate separation among vehicles under their control, much as they do today with radar-based surveillance. ADS-B data may also be recorded and downloaded for post flight analysis. The ADS-B system includes a certified source of navigation data (i.e., high-integrity GPS system), a transmitting system, a datalink and transport protocol and a receiving system. Examples of ADS-B data links include transponders operating at 1090 MHz, at 978 MHz or VHF.
ADS-B has many advantages over conventional surveillance techniques. It provides improved situation awareness, improved visibility, reduced environmental impact, and increased safety and efficiency. It has the potential to be more accurate than radar surveillance, which may allow aircraft to safely operate closer to one another in densely trafficked areas. It may be less costly to install and maintain than other forms of surveillance. It also has the potential to enable more efficient, faster and more robust decentralized separation assurance as compared to the conventional radar-based centralized separation assurance.
However, ADS-B as presently available faces a significant flaw, in that it relies on the accuracy of the navigation system of each vehicle and on the correct function of the ADS-B transmission equipment of each vehicle. If any of the equipment on any of the vehicles involved malfunction or be incorrectly configured, a real risk of collision is the result. Furthermore, should the navigation system onboard an aircraft fail, the current radar surveillance system provides a backup that can guide the aircraft; with ADS-B, there is no surveillance-based backup. Finally, it is possible to broadcast position reports unconnected to any real aircraft in an attempt to disrupt air traffic maliciously. Several patents have been filed or awarded to address some aspects of these weaknesses.
A number of patents and patent applications claim inventions that identify terrorist or otherwise dangerously controlled aircraft. US20110144897 describes systems and methods to track and identify suspect aircraft. US20100052973 describes a device and method to identify aircraft that pose a threat of collision on the ground. However, these systems and methods rely on the integrity of the navigation and surveillance systems comprising ADS-B.
US20110140950 describes an approach in which the recipient of an ADS-B position report compares the distance to the reporting vehicle, as determined by time-of-flight of the ADS-B transmission, with the distance to the reported position, and alerts if there is a significant discrepancy. This approach fails to detect a malfunction wherein both aircraft positions are erroneous but the calculated distance between them is not, such as could occur were both aircraft relying on the same erroneous means of navigation. It also fails to detect potential collisions with aircraft not transmitting ADS-B positions. It does not identify whether either of the two aircraft involved is broadcasting the correct position, nor does it identify which aircraft is broadcasting the wrong position if only one is. Finally, an erroneously broadcasting aircraft departing an airfield with little activity is likely airborne before the problem can be detected this way.
Similarly, US2011/0057830 describes systems and methods to validate suspect aircraft position reports by a group of receiving aircraft which communicate with each other to share observed relative positions to the suspect aircraft. In this way, the group can estimate position of the suspect aircraft and compare that position estimate to the position reported in the suspect's transmission. This approach is complicated, requires considerable additional communications bandwidth, and is unlikely to be implemented in time for the desired use of ADS-B. Additionally, it is unlikely to detect an erroneously broadcasting aircraft departing an airfield with little activity before it becomes airborne.
US20110163908 describes systems and methods to validate suspect aircraft position reports using direction finding equipment onboard the receiving aircraft. The complexity to implement additional directional antennas and direction-finding equipment onboard aircraft would pose some cost and logistical issues. This approach fails to detect a malfunction wherein both aircraft positions are erroneous but the calculated bearing between them is not, such as could occur were both aircraft relying on the same erroneous means of navigation. It also fails to detect potential collisions with aircraft not transmitting ADS-B positions. It does not identify whether either of the two aircraft involved is broadcasting the correct position, nor does it identify which aircraft is broadcasting the wrong position if only one is. Finally, an erroneously broadcasting aircraft departing an airfield with little activity is likely airborne before the problem can be detected this way.
U.S. Pat. No. 7,423,590 and application US20090009395 describe systems for authenticating aircraft identification and position transmissions by comparing them to a secondary position measurement source such as radar or multilateration. This solution would be expensive, in that one of the hopes with ADS-B is to eliminate costly surveillance systems. It fails to detect problems wherein an aircraft is not transmitting its position at all, and it does nothing to determine accuracy of the aircraft identification and type broadcast. Finally, an erroneously broadcasting aircraft departing an airfield with too little activity to justify a secondary position measurement source with coverage of the surface will be airborne before the problem can be detected this way.
U.S. Pat. No. 7,570,214 describes a method and a system for validating ADS-B transmitted positions against time of arrival of the ADS-B transmission at multiple locations. This approach suffers from similar shortcomings to those discussed above.
U.S. Pat. No. 7,383,124 describes an ADS-B monitoring device that “listens” to the aircraft's ADS-B transmissions and compares them to the signal sent to the ADS-B transponder for transmission. This system could detect some problems with the aircraft's ADS-B transmission equipment. However, it requires that yet another system be installed on the aircraft, and it does not detect errors in the signal sent for transmission, such as navigation system errors.
Accordingly, there is a need for an improved system and method for ensuring ADS-B integrity of departing aircraft that addresses the above mentioned problems.